This invention relates to the continuous production of foamed sulfur compositions.
U.S. Pat. No. 3,337,355 covers a method of producing sulfur foams which comprises generally the steps of heating elemental sulfur to above its melting point, blending a stabilizing agent and a viscosity increaser into the molten sulfur and forming bubbles in the molten sulfur and cooling it below its melting point. Bubble formation is accomplished by introducing into the sulfur containing the viscosity increaser and stabilizer a quantity of a foaming agent such as a mixture of phosphoric acid and sodium carbonate or an organic foaming agent such as N,N'-dinitrosopentamethylene tetramine. In the illustrated production of foam the foaming agent is introduced into the modified molten sulfur in a vessel and the resulting foam is passed from the vessel through a conduit and deposited where desired.
While this method of forming sulfur foam may be suitable for batch applications and those applications in which portability of the apparatus is not important, in certain applications where it is desired that the process be continuous and/or that the apparatus be movably mounted to deposit a continuous layer of foam as, for example, from a constantly moving truck, it is desirable that the blending of the molten sulfur with the viscosity improver and the stabilizer be separated from the addition of the foaming agent.
It is also desirable to apply a continuous process to the generation of other sulfur based foams such as those illustrated by those described in commonly assigned U.S. patent application Ser. Nos. 253,144 and 344,694, which employ as the basic foaming materials mixtures of sulfur and ring hydroxy or ring amino-substituted aromatic polysulfides. The mixtures are foamed and cross-linked by the addition of an organic acid, preferably a carboxylic acid, and a polyisocyanate or polyisothiocyanate. Since the aromatic polysulfide contains hydroxy or amino groups which will react with isocyanates, prior addition of the acid to the molten sulfur-aromatic polysulfide mixture is required. Additionally, in many cases, the acids which are employed are incorporated into the polysulfide chains; and when polyisocyanate is added, the reaction produces CO.sub.2 (or COS with polyisothiocyanates) causing foam formation, and the reaction of the carboxyl and isocyanate groups gives additional polymer cross-linking by amide formation (in addition to the urethane or ureido formation with the hydroxyl and amino groups of the polysulfide).